Safety valve



Oct. 11, 1966 j L R 3,277,912

SAFETY VALVE Filed Dec. 9, 1963 5 Sheets-Sheet 1 76 INVENTOR JULIUS F. MELZER 5%;5 LjMW/AW ATTORN EY Oct. 11, 1%6

Filed Dec. 9, 19'53 SAFETY VALVE 5 Sheets-Sheet 3 g 62 N 1 551 3 32 a 6 @2 1 a Y a I a w l INVENTOR JULIUS EMELZER ATTORNEY J. F. MELZER SAFETY VALVE Oct. 11, 1966 5 Sheets-Sheet 5 Filed Dec. 9, 1965 0 w m Q m M 2 M w 4 2 INVENTOR JULIUS F MELZER WW ATTORNEY Oct. 11, 1966 J. F. MELZER 3, 77,

SAFETY VALVE Filed Dec. 9, 1963 5 Sheets-Sheet 4 191 12 INVENTOR JULIUS F MELZER iBYp/M/W ATTORNEY Oct. 11, 1966 SAFETY VALVE Filed Dec. 9. 1963 5 Sheets-Sheet 5 INVENTOR JULIUS F MELZER ATTORNEY .J. F. MELZER 3,277,912 I United States Patent 3,277,912 SAFETY VALVE Julius F. Melzer, 544 King St., Port Chester, N.Y. Filed Dec. 9, 1963, Ser. No. 330,519 8 Claims. (Cl. 137-73) This application is a continuation-in-part of my prior application Serial No. 294,472, filed July 12, 1963, and now abandoned.

The present invention relates to boiler safety valves and more particularly to such valves as contain a plurality of independent heat and/ or pressure sensitive devices to increase the factor of safety.

An object of the present invention is to minimize the possibility of excess pressures being developed in a steam or hot water boiler.

Another object of the present invention is to give positive visible and aural signals of overheating of a boiler.

Still another object of the present invention is to enable quick and reliable tests of the condition of such valves.

Still a further object of the present invention is to provide a sefety valve which will perform its intended function in spite of corrosion in the valve seat or the buildup of mineral deposits resulting from the use of hard water in the boiler.

The foregoing objects and others which may appear from the following detailed description are attained, in accordance with principles of the present invention, by providing the usual poppet valve in a pressure relief or safety valve with a number of alternate or ancillary steam passages between the boiler and the vent stack, normally closed olf by a fusible alloy. The fusible alloy is so formulated as to have a melting point a few degrees above the temperature of steam at the pressure at which the safety valve is designed to blow-off. Since the valve is usually vented to the exterior of the building or room in which the boiler is located, through a vent pipe or vent stack, it is possible that the rupture of the fusible alloy would go unnoticed for some time so I provide a number of auxiliary vent paths normally closed off and exhausting directly into the boiler room. Those vents open at the same time as the main vent, allowing relatively small jets of steam at high velocity to be vented into the room. The noise of such venting and the plumes or jets of steam audibly and visually inform the attendant that failure has taken place so he can take appropriate steps to correct the cause of failure and shut down the boiler.

In one form of my invention the poppet valve head itself is provided with through holes which are normally blocked off as by filling them with a fusible alloy. The alloy is compressed into place, or peened all over after having been melted into place to make sure that it is homogeneous in texture so that the intended strength is attained. Preferably the holes into which the alloy is cast have peripheral steps so that the alloy is formed with marginal flanges to hold it in place more effectively. Alternatively the holes in the valve may be covered with a sheet of brass or similar metal on the low pressure side of the valve disk and soldered into place with the desired alloy.

Further modifications comprise substituting a crownlike brass valve seat against which the valve disk rests and filling in the spaces between the prongs or fingers of the crown with the fusible alloy. Thus if the valve disk refuses to lift oi the seat under excess pressure conditions the alloy melts and allows the steam to escape between the remainder of the seat and the valve disk.

In one modification the poppet valve is provided with an exterior operating handle which can be manually operated to test the valve to see that it has not become stuck in the seat.

3,277,912 Patented Oct. 11, 1966 "ice In all modifications, simple disassembly means are provided so that the holder for the fused alloy may readily be removed and a new one mounted when it should become necessary.

All modifications include the auxiliary steam passages venting directly into the boiler room in order to give the audible and visible alarm referred to above and all modifications also include simple reliable means for replacing the fusible alloy plugs in the alarm arrangement.

Additional safety means in the line of an automatically operated switch responsive for initiating shut down of the boiler may also be provided.

The present invention will be more fully understood by reference to the following detailed description which is accompanied by a drawing in which:

FIGURE 1 illustrates in fragmentary form a steam or hot water boiler which is to be protected, together with a safety valve, embodying one form of the present invention and various outlet pipes adapted to carry steam or hot water to utilization means;

FIGURE 2 illustrates a vertical cross sectional view of one embodiment of the present invention;

FIGURE 3 is a plan view of the valve head of my invention as arranged in the embodiment of FIGURE 2, while FIGURE 4 is a bottom plan view of the valve head of FIGURE 3 without the alloy filling;

FIGURE 5 is a fragmentary cross sectional view taken along line 55 of FIGURE 4;

FIGURE 6 illustrates a vertical cross sectional View of another embodiment of the present invention;

FIGURE 7 illustrates in vertical cross section a further embodiment of the present invention;

FIGURE 8 illustrates, in fragmentary, vertical cross section, a still further modification of FIGURE 7, while FIGURE 9 is a vertical cross sectional view of yet another modification of the embodiment of FIGURE 7;

FIGURE 10 is a perspective view, partly in section, of still a further modification of the present invention.

FIGURE 1 shows part of a steam or hot water boiler 10 having mounted thereon various outlet pipes 12, 14 through which steam or hot water, heated in boiler 10, is conducted to various utilization devices as indicated by the arrows. Boiler 10 is also provided with improved safety valve 16 according to my invention, having a vent pipe 18 through which steam is passed to the exterior of the building when excess pressure develops in boiler 10. Valve 16 is also provided with alarm vents 20 which vent steam jets into the boiler room when the alloy plugs melt, thus warning the attendant that such failure has occurred.

Valve 16, as more fully shown in the sectional view in FIGURE 2, comprises a casing 22 having an inlet neck section 24 having screw threads 26 by means of which it may be installed in boiler 10. Inlet section 24 has threads 28 at the end opposite the portion carrying threads 26 onto which is screwed outlet body portion 30. This portion has a side neck 32 having threaded aperture 34 into which outlet vent pipe 18 (FIG. 1) may be received. Outlet portion 30 has an opening 36 coaxial with inlet portion 24 into which is inserted plug 38 carrying central valve stem guide 40 having a central bore. Plug 38 is secured in place with a number of set screws 42 threaded through equally spaced radial openings in body 30.

Valve 16 when assembled is generally of a T formation, inlet portion 24 and outlet portion 30 forming the arms of the T and neck 32 forming the leg of the T.

Inlet portion 24 is provided with an upper wall 42 having a central aperture 44 which together with valve head 46 divide the interior into inlet and outlet chambers.

An O-ring gasket 48 is fitted into an annular groove in the central aperture to cooperate with valve head 46 to form a steam and water tight seal.

Valve head 46 has a central hub portion 50 with a central bore 52 into which is secured one end of valve stem 54. It is preferably secured in place with a nut 56 screwed onto a threaded portion of stem 54 and the stem lightly peened over to prevent nut 56 from running off. Since the junction between head 46 and stem 54 must be 'ght, bore 52 should closely fit the stern and if desired a sealing washer 58 may be interposed between nut 56 and valve head 46.

Stem 54 passes through valve bushing 40 to the exterior of the valve and also passes through a hole in lifter arm 60. Lock nuts 62 are screwed on the upper end of stem 54. By pressing downward on the free end of arm 60, valve head 46 may be lifted off its seat against the pressure of spring 64 coaxially mounted about bushing 40.

Preferably, a cup washer 66 is interposed between spring 64 and valve head 46 for a purpose to be later discussed.

The pressure of spring 64 against valve head 46 may be adjusted within limits by loosening set screws 42 and pressing plug 38 more or less into body 22 and then retightening set screws 42.

If desired lubricant retaining grooves 68 may be provided on valve stem 54.

Referring now more particularly to FIGURE 4 it will be seen that valve head 46 has central hub 50 and an outer rim portion 70. Rim portion 70 has a fiat outer flange 72 and a tapered rim 74 which is adapted to seat against ring 48 (FIG. 2).

Between rim portion 70 and hub 50 is an intermediate portion 75 of lesser thickness than rim portion 70 and embodying a number of radially arranged spokes 76. As shown by the partial sectional view in FIGURE spokes 76 are preferably deltoid or keystone-shaped in cross section, with the apex of the deltoid facing in the direction toward the inlet side of the valve. Intermediate portion 75 is filled with a low melting point alloy. Such portion is filled in level with the thickest portion of rim 70 completely surrounding spokes 76. The alloy is poured into place while molten and then hammered or rolled to compress it to assure that it is of uniform density throughout. The alloy is so compounded that it will soften or melt at a temperature about five degrees Fahrenheit higher than the temperature equivalent to the pressure at which valve 46 is designed to lift off sealing ring 48.

For example, if the normal let-off pressure for the valve head is pounds per square inch, an alloy of 55% bismuth and 45% lead will melt at 250 which corresponds to a saturated steam pressure of pounds per square inch. If the normal let-off pressure is 40 pounds per square inch a 60% bismuth and 40% indium alloy may be used. This alloy melts at 291 corresponding to a steam pressure of 45 pounds per square inch.

Similar examples for higher temperatures and pressures are:

Pressure, lbJin. Temperature, Composition degrees 50 300 Pure Indium. 100 340 55% Lead, 45% Tin. 150 361 38% Lead, 62% Tin.

210 392 91% Tin, 9% Zinc.

which might tend to undesirably weaken its resistance to steam pressure.

Now if due to corrosion of the parts or mineral deposits between rim 74 and valve seat 48, the valve does not open at the predetermined pressure to relieve boiler 10, a continued increase in the temperature of the steam will melt alloy 78 thus venting the boiler through vent pipe 18.

The invention further contemplates the addition of a plurality of fusible plugs 80 screwed into tapped holes in inlet body 24. Each of these has a restricted through bore 82 into which is cast plug 84 of a fusible alloy melting at the same temperature as alloy 78. Thus when alloy 78 melts due to excessive temperatures, plugs 84 also melt, releasing limited amounts of steam directly into the boiler room. The plumes of steam and the noise caused by the escape of steam serve as an instantaneous and readily noticed alarm that some malfunction has taken place, which must be corrected.

Referring now to FIGURE 6 which shows a modification of the invention so far described, body casing 102 is provided with an inlet neck portion 104 carrying threads 106 adapted to be fitted into the outlet of boiler 10 (FIG. 1). In this modification the inlet neck section is integral with body portion 110. The body portion has a side neck 112 having a threaded aperture 34 into which outlet vent pipe 18 (FIG. 1) may be screwed. Body portion has an opening coaxial with inlet neck portion into which is screwed plug 116 provided with a central bore through which passes valve stem 118. Plug 116 is provided with an accurately concentric machined bore 120 which serves as a guide for valve head 122. Valve head 122 is generally cup-shaped in formation, having an inner central coupling lug 124 which is coupled to valve stem 118 by means such as a through pin 126 passing through aligned apertures in lug 124 and valve stem 118.

Valve stern 118 is concentrically surrounded by valve spring 64, one end of which bears against the inner side of plug 116 and the other end of which bears against cupped washer 128 which engages the upper surface of knuckle 119 formed along valve stem 118 just above its point of attachment to valve head 122.

In this modification the outside base of cup shaped valve head 122 bears against a removable valve seat 129 screwed into internal threads 130 in a reduced portion of body 102 separating the valve into inlet chamber 132 and outlet chamber 134.

Valve seat 129 is annular or ring shaped in plan, having threads on its outer periphery adapted to engage with threads 130, and has an upstanding inner ring-like lip portion 136 having a serrated or sinuous upper edge. It is also provided with a shorter upstanding outer rim portion 138 and the space between outer rim 138 and innerlip 136 is filled with a low melting point alloy 140. Its composition and melting point are determined as described above with reference to alloy filling 78. Thus when the valve is in use, operating under normal boiler pressures and temperatures, valve head 122 bears against a smooth uniform sealing lip along the inner lip 136. Should the valve refuse to operate under excessive temperatures or pressures, alloy 140 will melt, thus opening a series of generally V-shaped apertures around the periphery of the inner rim and allow steam to escape vent side neck 112.

At the same time alloy 84 in plugs 80 (one is shown) screwed into tapped holes in the outer periphery of body 110, melts and allows the escape of steam into the boiler room thus notifying the operator that corrective action must be taken. Since in this modification plugs 80 are in communication with the outlet passage they will melt later than alloy 140 providing a moderate time delay which may be desirable. Alternatively alloy 84 may have a slightly lower melting point so it will release as soon as steam passing under valve head 122 strikes it.

In the modification of FIGURE 7, the general construction of the valve body 110, valve head 122 and valve spring assembly is the same as in FIGURE 6 so they will not again be described in detail. However, in this modification, valve seat 142 is constructed of a single metal such as brass or stainless steel selected for its stability and resistance to corrosion.

Body is provided with a side tapped hole or passage 146 communicating with inlet chamber 132. Attached to said passage by means of a hollow cap screw 150 is a hollow L-shaped vent member 148. Central bore 152 of cap screw 150 is plugged at its inner end with fusible alloy plug 84, while radial holes 154 provide communication between central bore 152 and the interior hollow of L- shaped member 148 no matter what orientation is attained by cap screw 150 as member 148 is screwed to body 110. The open top of member 148 may be closed off with a thin brass plate 158 to prevent entrance of dirt, moisture, etc., into the hollow interior thereof. It should be so lightly secured in place, as by a light press fit, as to be instantaneously removed by boiler pressure against its interior surface, should alloy 84 melt.

If desired, a valve head assembly such as shown in FIGURE 8 may also be used in this modification of FIG- URE 7. Here valve head 122 is provided with a number of through bores 160 arranged in a circle about central lug 124, and these holes are closed off by a relatively thin brass disk 162 soldered to the inner surface of valve head 122 by a solder comprising an alloy selected as described above with respect to alloy 78, 84. The solder is indicated at 164. Preferably, disk 162 has a narrow upstanding rim 166 to provide additional soldering area and to increase the rigidity of the disk. Nevertheless this disk is fragile enough that when the solder melts, the boiler steam pressure deforms it and ruptures it so that it folds up around spring 64 to allow escape of the steam. In this modification, valve head 122 must be provided with a number of holes 168 assuring communication between outlet chamber 134 and the space behind valve head 122.

The modification of FIGURE 9 is generally similar to that shown in FIGURE 7 except side bore 146, in communication with chamber 132, has a side leg 170 directly communicating with outlet chamber 134.. Hollow stud 172, having a central bore 174 plugged at its inner end with alloy plug 84, as in the case of cap screw 150, has a number of radial holes 176 assuring communication between central bore 174 and side leg aperture 170 no matter what the orientation of stud 172. Stud 172 is also provided with a number of apertures 178 at its end enabling the escape of steam directly into the boiler room upon failure of alloy 84 as well as exhausting into outlet chamber 134. plugs may be placed in apertures 178 so as to prevent escape of steam into the boiler room upon normal operation of the valve. Thus no alarm is given for normal operation of the safety valve but the higher temperature steam resulting from failure of valve head 122 to lift off its seat which causes alloy 84 to melt will also melt the plugs 178a and give an alarm. In addition an additional alarm may be provided by pressure sensitive switch 180 screwed into tapped hole 182 directly communicating with chamber 132. The pressure sensitive switch may include a sylphon bellows 184 having its interior in communication with chamber 132 and a switch 186 adapted to be connected to an alarm or central circuit. Switch 186 is shown as a single pole double throw switch having one normally closed and one normally open circuit but it should be apparent that either the normally closed or normally open circuit mode may be used alone to either close a circuit on the occurrence of excessive pressure or to open a circuit. The alarm circuit (not shown) may either energize a light or alarm bell or shut down the electrical circuit which runs the burner associated with the boiler.

A further modification has also been shown in the construction of the valve seat which is equally applicable If desired, as shown at 178a alloy to the modifications of the member shown in FIGURES 7 and 8. In this modification the Valve seat comprises a threaded ring 190 adapted to be screwed into threaded aperture 130. It has a circular inner bore having a conical face 192 at its lower end. Closely but removably fitted within the central bore is a seat ring 194 having a lower flare corresponding to countersink 192. The upper end of ring 194 serves as the seating surface for valve head 122. Should the seating surface become rough or corroded, it is relatively inexpensive to remove ring 190, slip out seat ring 194 and remount the assembly in aperture 130. The seat ring may readily be made of truly cut sections of brass tubing without expensive threading and boring operations. It is only necessary to provide the flare by means of a simple flaring or spinning operation.

The further modification shown in perspective, and in partial section, in FIGURE 10 comprises a unitary valve body casing 102 provided, as in previous embodiments, with an inlet neck portion 104 carrying threads 106 adapted to be fitted into the outlet of boiler 10 (FIG. 1). As in the modification of FIGURE 9, body portion 102 has a side neck 112 having a threaded aperture 34 into which the outlet vent pipe may be secured. Upper body portion 110 has an opening coaxial with inlet neck portion 104 into which is screwed plug 116 provided with a central bore through which passes valve stem 118.

Plug 116 is provided with an accurately concentric machined bore 120 which serves as a guide for valve head 122.

Valve head 122 is generally cup-shaped in formation having an inner central coupling lug 124 coupled to valve stem 118.

Valve stem 118 is concentrically surrounded by valve spring 64, one end of which bears against the inner side of plug 116 and the other end of which bears against cup washer 128 which engages the upper surface of knuckle 119 formed along valve stem 118 just above its point of attachment to valve head 122.

The outside base of cup-shaped valve head 122 bears against a removable valve seat 194a secured in place in threaded body portion of body 102 separating the valve into inlet chamber 132 and outlet chamber 134. Valve seat 194a is, as in the case of FIGURE 9, secured in place by a threaded ring 190 screwed into threads 192.

Immediately below outlet chamber 134 is provided an auxiliary chamber 200 in communication with chamber 134. Wall 202 is provided with a number of threaded apertures 204 into which are threaded plugs 206 having central bores 208 into which are cast plugs of alloy 78 as previously described. Apertures 204 provide a direct path of communication between inlet chamber 132 and outlet chamber 134 when the alloy 78 melts. If desired, O-ring gaskets such as that shown at 210, may be provided between the body of plugs 206 and the apertures 204 in order that the seal may be steam tight.

Immediately below outlet 34 chamber 200 is provided with an auxiliary opening 212 communicating with the exterior of the valve. Said opening is normally closed by a plate 214 resiliently held in place by cap screws 216 screwed into threaded apertures 218. Each cap screw (only one is shown) has interposed between its head and plate 214 a coil spring 220. Said springs lightly press plate 214 against the opening 212, maintaining the opening closed unless the safety valve blows or excess temperatures or pressures cause alloy 78 to melt.

Should either of such events occur, the pressure of steam against the inner side of plate 214 causes it to lift away from the lips of opening 212 and allows the escape of steam into the boiler room. The noise of the steam escaping between the plate and the lips of opening 212 constitutes a readily detectable indication that the boiler requires attention.

Also, if it should become necessary to inspect the condition of fusible alloy 78 or to replace plugs 206 it is a simple matter to unscrew one of screws 216, swing plate 214 out of the way and inspect or replace as necessary. Preferably, apertures 204 and plugs 206 are of such diameters and so threaded that other plugs cannot be substituted, thus defeating the safety features provided by my invention.

As is the case with the modification of FIGURE 2, the modification of FIGURE 10 is provided with a test lever 60a secured to valve stem 118 by a threaded through pin 222. Roller cam faces 224 on either side of stem 118 carried by lever 60a bear against the top of plug 116 and if lever 60a is either lifted or depressed forcibly, stern 118 is lifted against the pressure of spring 64 causing steam within the boiler to be vented into space 134. Thus the operator may periodically check to be sure that valve 122 has not become frozen or stuck against valve seat 194a.

Having now particularly described several embodiments of the present invention and the best manner of practising the same, what I claim as my invention is:

1. A safety valve including a body casing having an inlet sect-ion adapted to be fitted to a steam boiler, an outlet section adapted to be coupled to a vent pipe, a wall between said sections containing a circular valve seat, a valve head pressed against said seat by a compression spring within said outlet section, a valve stem connected to said head at a control portion thereof coaxially arranged within said spring and extending to the exterior of said casing through a guide bushing secured to a wall of said casing, a number of passageways bypassing said valve head and normally closed with the aid of a metal alloy adapted to melt at a temperature corresponding to a steam pressure within said boiler below the maximum for which said boiler is designed but over the pressure at which said safety valve is designed to operate and at least one additional passageway in said body casing directly venting into the immediate space about said boiler, each of said additional passageways being normally closed oif with plugs of said fusible alloy so that when said boiler is vented through said valve an audible and visible alarm is given.

2. A safety valve as set forth in claim 1 in which said valve head comprises an annular circumferential rim and a perforated intermediate .portion between said rim and central portion, a metal disk secured against said valve disk on the side remote from said inlet section by said fusible metal alloy.

3. A safety valve including a body casing having an inlet section adapted to be fitted to a steam boiler, an outlet section adapted to be coupled to a vent pipe, a wall between said sections containing a circular valve seat, a valve head pressed against said seat by a compression spring within said outlet section, a valve stem connected to said disk at a central hub portion thereof coaxially arranged within said spring and extending to the exterior of said casing, said head being cup shaped and comprising an annular circumferential rim and a perforated intermediate portion between said rim and said central hub, a thin disk of metal lying within said cup and overlying said perforations, said disk being soldered to the inside of said cup with a metal alloy adapted to melt at a temperature corresponding to a steam pressure within said boiler below the maximum for which said boiler is designed whereby said solder melts if excess pressures occur in said boiler, and a number of auxiliary passages through the wall of said casing into said inlet section each of said passages being fitted with a plug having a bore filled with said metal alloy, the melting of said alloy in said plugs allowing steam from said boiler to escape directly into space surrounding said boiler.

4. A safety valve as set forth in claim 3 wherein the rim of said cup is provided with a number of apertures providing communication between the interior of said cup and said vent pipe,

5. A safety valve including a body casing having an inlet section adapted to be fitted to a steam boiler, an outlet section adapted to be coupled to a vent pipe, said body casing being of substantially T shaped formation, one arm of said T being adapted to be connected to said boiler, a wall within said body casing between said one arm and the leg of said T dividing said casing into inlet and outlet portions, a valve seat in said wall, a removable plug in the other arm of said casing having a centrally located valve stem guide member, a valve disk in engagement with said valve seat, a valve stem coupled to said disk and passing through said guide member to the exterior of said casing, a compression spring surrounding said guide member and valve stem and pressing said disk into engagement with said seat, said disk having an annular rim, a central hub portion and an annular intermediate part of reduced thickness relative to said rim, said intermediate portion including a number of radially extending spokes of deltoid formation, a fusible metal alloy filling said annular intermediate portion, the narrower edges of said spokes being on the side of said disk adjacent said inlet section, and a number of relatively small auxiliary passages through the wall of said body casing into said inlet portion, each of said passages being fitted with a plug having a central bore filled with said metal alloy, the melting of said alloy in said plugs allowing steam from said boiler to escape directly into space surrounding said boiler.

6. A safety valve including a body casing having an inlet section adapted to be fitted to a steam boiler, an outlet section adapted to be coupled to a vent pipe, said body casing being of substantially T shaped formation, one arm of said T being adapted to be connected to said boiler, a wall within said body casing between said one arm and the leg of said T dividing said easing into inlet and outlet portions, a valve seat in said wall, a removable plug in the other arm of said casing having a valve guide member, a valve head in engagement with said valve seat, a compression spring pressing said head into engagement with said seat, said valve seat comprising a threaded ring screwed into said wall and a tubular valve seat member secured by said ring into said wall, and at least one relatively small auxiliary passage through the wall of said casing into said inlet portion, said plug also having a passageway from said central bore to said outlet portion, each of said passages being fitted with a plug having a central bore closed off with said metal alloy, the melting of said alloy in said plug allowing steam from said boiler to escape directly into space surrounding said boiler.

7. A safety valve including a body casing having an inlet section adapted to be fitted to a steam boiler, an outlet section adapted to be coupled to a vent pipe, a wall between said sections containing a valve seat, a valve head pressed against said seat by a compression spring within said outlet section, a valve stem connected to said head at a central portion thereof coaxially arranged within said spring and extending to the exterior of said casing through a guide bushing secured to a wall of said casing, a number of passageways bypassing said valve head and normally closed with the aid of a metal alloy adapted to melt at a temperature corresponding to a steam pressure within said boiler below the maximum for which said boiler is designed but over the pressure at which said safety valve is designed to operate and at least one additional passageway in said body casing directly venting into the immediate space about said boiler, said additional passageway being normally closed olf -by means which will release steam into said immediate space when said alloy is melted.

8. A safety valve including a body casing having an inlet section adapted to be fitted to a steam boiler, an outlet section adapted to be coupled to a vent pipe, a wall between said sections containing a valve seat, a valve head pressed against said seat by a compression spring within said outlet section, a valve stem connected to said head at a central portion thereof coaxially arranged within said spring and extending to the exterior of said casing through a guide bushing secured to a wall of said casing, a number of passageways bypassing said valve head and normally closed with the aid of a metal alloy adapted to melt at a temperature corresponding to a steam pressure within said boiler below the maximum for which said boiler is designed but over the pressure at which said safety valve is designed to operate and at least one additional passageway in said body casing directly venting into the immediate space about said boiler, said additional passageway being normally closed off by means which will release steam into said immediate space when said alloy is melted, said means including a plate normally closing said passageway but adapted to be lifted to clear said passageway by pressure of steam vented from said boiler thereby giving an audible and visible alarm.

References Cited by the Examiner UNITED STATES PATENTS Palmer 137-73 Smith 137--73 Holmes 137-73 Hamilton 13774 X Twigg et al. 137-72 X Friedman 137-73 X Parker 13773 Watkins 137-73 Switzerland.

15 M. CARY NELSON, Primary Examiner.

HENRY T. KLINKSIEK, Examiner. 

1. A SAFETY VALVE INCLUDING A BODY CASING HAVING AN INLET SECTION ADAPTED TO BE FITTED TO A STEAM BOILER, AN OUTLET SECTION ADAPTED TO BE COUPLED TO A VENT PIPE, A WALL BETWEEN SAID SECTIONS CONTAINING A CIRCULAR VALVE SEAT, A VALVE HEAD PRESSED AGAINST SAID SEAT BY A COMPRESION SPRING WITHIN SAID OUTLET SECTION, A VALVE STEM CONNECTED TO SAID HEAD AT A CONTROL PORTION THEREOF COAXIALLY ARRANGED WITHIN SAID SPRING EXTENDING TO THE EXTERIOR OF SAID CASING THROUGH A GUIDE BUSHING SECURED TO A WALL OF SAID CASING, A NUMBER OF PASSAGEWAYS BYPASSING SAID VALVE HEAD AND NORMALLY CLOSED WITH THE AID OF A METAL ALLOY ADAPTED TO MELT AT A TEMPERATURE COORESPONDING TO A STEAM PRESSURE WITHIN SAID BOILER BELOW THE MAXIMUM FOR WHICH 